actually after the third time they won't be able to unsuspend themselves.
They need to request it, in most cases we do unsuspend the account, with a few conditions (like they need to try and resolve the cause).
I see that your site consists of a forum, do you have any plugins that might be badly coded?
It's not one file causing it, I saw a few of them mentioned in the log. The main problem would be that it was using 25 processes at the same time.
The most frequent files from the log are showthread.php and xmlhttp.php, so if you have mods that affect them that would be a good place to start looking.